The present invention relates to the field of optical data processing.
Homodyne and heterodyne detection is one of the most important concepts in information processing theory. Several other concepts are associated with it, such as phase-sensitive detection, lock-in detection, frequency and time-division demultiplexing and base-band demodulation, time-integrative correlation, and many other devices, which can be fined the literature; see A. B. Carlson), communication systems: An introduction to signal and noise in electrical communication, 2 Edition (MaGraw-Hill, New York 1975)
These concepts have been used extensively in designing many electronic devices. For example the lock-in amplifier is used routinely in many microscopic and tomographic systems, see xe2x80x9cKyuman Cho, David L. Mazzoni and Cristopher C. Davisxe2x80x9d Measuring of the local slope of the surface by vibrating-sample heterodyne interferometery: new method in scanning microscopy, Kyuman Cho, David L. Mazzoni and Cristopher C. Davis)(for as a data acquisition tool, further they are often used in pulling the signal which is embedded in very high noise environment (reference in noise reduction within signals) (M. L. Mead, Lock in amplifier: Principles and applications, (Peregrinus, London 1983). Lock-in detection is also used in controlling machine vibrations, and components within servo systems for tracking CD, DVD and magneto-optics disk; references problems of tracking: Casimer Maurice DeCusatis, Lawrence Jacobowitz, xe2x80x9cActive Tracking system for optical disk storage,xe2x80x9d U.S. Pat. No. 5,793,718. See also Hubert Song et al. Non-contact servotrack writing with phase sensitive detection,xe2x80x9d U.S. Pat. No. 5,991,112. Time integrative correlators are used in pattern recognition devices; e.g. applications involved in identifying a specific optical bit pattern for header recognition or code-division demultiplexing, or data base search in high speed optical communication systems or soft ware applications. See Jun Shan (Optical bit pattern recognition by use dynamic grating in erbium doped fiber) Optics letters, Volume 22, 1757-1759 (1997) Frequency and time-division, base band demodulators are also some of the most important components used for constructing telecommunications systems, networking, cable TVs. See A. B. Carlson, communication systems: An introduction to signal and noise in Electrical communication, 2 Edition (MaCraw-Hill, New York 1975).
In the recent years much attention has been devoted to the use of wavelength division demultiplexer as one of the main components for telecommunication systems base on fiber optics. See for example Optical Networking Volume 1 Januray 2000). See also the following U.S. patents: Optical Add-Drop multiplexer compatible with very dense WDM optical communication systems. U.S. Pat. No. 5,982,518 Nov. 9, 1999; Li xe2x80x9cWavelength and Bandwidth tuneable optical system,xe2x80x9d U.S. Pat. No. 5,841,918. This patent discloses a tunable Bragg cell; see also Daniel J. Fritz, Timothy J. Bailey and Mass Gary, xe2x80x9cAll Fibre wavelength selective optical switch,xe2x80x9d U.S. Pat. No. 5,446,809.
Wavelength division demultiplexing not only important for telecommunication but it has significant applications in other areas including biomedical applications, remote sensing, multispectra and hyperspectra pattern recognition and fiber sensors. Wavelength division demultiplexers can employ a Fabry-Perort interferometer, including MEMS structures, Bragg Grating either in fiber, volume holographic materials, or fabricated structure for layers of Electro-optic materials, and a Mach_Zender interferometer. See the following material in Optical Society of America: Handbook of Optics, volume I and II. For enhancing the capability of transferring the data in telecommunication systems, most recently it was proposed to combine either wavelength division multiplexing (WDM), with either time (TDM) or frequency multiplexing (FDM). In the receiving end it was proposed that the wavelength demulteplexing is done optically and time or the frequency division demultiplexing is done electronically.
I believe that up until now, no one optical device is present in the prior art which can do both of these operations simultaneously. I introduce a new device concept herein that can be utilized for combining both WDM and FDM or TDM demulteplexing on the same device. I name the new device HTWDM (heterodyne time wavelength division demultiplexing), because the new device not only combines WDM with FDM or TDM, but it can combine other homodyne detection functionality with wavelength division demulteplexing functionality. In more general terms my invention can combines K-vector demultiplixing with heterodyne detection (k vector division demultiplexing will be illustrated further through the text of this invention). This combined functionality has enormous significance for many applications.
I introduce herein a general concept for homodyne and heterodyne detection based on K-vector tunable optical cells. An important application is use of the optical cells as wavelength-division demultiplexers (or in more general terms K vector division demultiplexers and mixing for homodyne heterodyne detection or time division demultiplexing will be performed in accordance with the present preferred inventive emdodiments on a single optical component. This component can operate as a low pass filter if the modulation is very fast. This is in contrast with the distributed Bragg reflector laser structure of U.S. Pat. No. 5,020,153 of Choa et al. whose invention is limited to WDM (not K-vector demultiplixing) and heterodyne detection, without any consideration for time division demultiplixing. Further in the Choa patent, each of the operations of WDM and heterodyne detection were performed in separate components within the integrated device. The Chao grating was used for WDM, whereas the heterodyne signal detection was produced by mixing the signal being detected with an external beat signal. In contrast with Chao, who discloses using distributed bragg grating within his device, the K vector selector can take numerous forms as will be illustrated. Thus the present invention can have numerous application in variety of areas ranges from telecommunication, tracking in CD and DVD, fluorescent microscopy; see M. Schrader and S, W. well, S. W. Hell, H. T. M. Van der Voort, xe2x80x9cThree-dimensional super-resolution with 4-PI-confocal microscopes using image restoration,xe2x80x9d Journal of applied physics, 84, 4033-4041 (1998) or in Foliage averaging; see Part 1: Foliage Attention and Back scatters Analysis of SAR images, J. G. Fleischman, S. Ayasli, E. M. Adams, D. R. Gosselin. IEEE transaction on aerospace and electronic systems, Vol.32, No 1 January 1996 P 135-144; or for applications in Lidar (light wave radar); see J. G. Fleischman, S. Ayasli, E. M. Adams, D. R. Gosselin Part III: Multi channel Whitened of SAR imagery IEEE transaction on aerospace and electronic systems, Vol.32, No 1 January 1996 P 156-164). In this invention also I propose a gratings to be tunable over wide range, these grating can be integrated within the structure of distributed feed back laser or vertical cavity lasers for enhancing the range of tunabiliy. It can also serve as part of add/drop demultiplexer. Other uses of the present invention include microscopic and tomographic sytems, multispectra and hyperspectra pattern recognition, non-destructive testing instruments, atmospheric turbulence correction devices, remote sensing systems and velocity measuring devices.
The significance of the present invention in connection with various applications can be understood as follows: (1) In Telecommunication for increasing the channel capacity of LAN (Local area net work and WAN (wild area net work), TV Cables, Telemetry systems. (2) In all forms of homodyne and heterodyne microscopy and tomography imaging for enhancing sensitivity, which can be achieved by averaging the measurement at various wavelengths. (3) In nondestructive testing, for controlling the operation of several machines, in which each wavelength is utilized to probe the operation of one machine. (4) In high precision Lidar probing and velocimetry which may be achieved via averaging the homodyne measurement over several wavelengths (5). Data fusion for multispectra and heyperspectra pattern recognition (6). Fluorescent microscopy and tomography (7) In the last three (4,5,6) by performing spectroscopic correlation as what have been explained in my previous patent on medical diagnostics (7). In atmospheric turbulence correction providung diversity in measuring the atmospheric aberration at different wavelengths and for CD and DVD applications for the purpose of Pick-up and tracking and switching on different drive, in which a one wavelength is used to read each drive. (8) It can also serve as part of an add/drop demultiplexer or (9) as components within the optical MODEM.
The combination of wavelength division demultiplexing and homodyne detection can be done in a variety of architectures depending upon the specific application and need. It can be structures from one cell, from combinations of fiber tunable cells, volume tunable cells, volume and fiber tunable cells, array of tunable cells, in an interconnect within a network architecture. This architecture can be used within WAN and LAN networking using all the well known topologies such as Bus, Tree, Ring Star; see xe2x80x9cLocal and metropolitan Area Networkxe2x80x9d, William Stallings, fifth edition, Prentice Hall 1997). Or can be integrated on one substrate. For example, for telecommunication applications or endescopic applications, one would more naturally consider the possibility of using fiber optical devices, or micro machined devices such as MEMS. For imaging purposes such as parallel microscopy, tomography, atmospheric turbulence correction one would consider the possibility of using volume devices or arrays of micromachined tunable filters. For conventional microscopy as well as for reading, writing, and tracking purposes of CD, DVD and magneto-optics, we will introduce a new holographic tunable cell design. This tunable cell should have ability of focusing light as small as 10 nm. This should provide, for the first time, an optical microscopic design (not a near field optical microscopy design) which can detect objects in the atomic level scale, while the tunable cell will function. simultaneously as a probe as well as the diagnostics tool. If a similar design is used for optical data storage, then this tunable cell should allow recording 105 M bite/cm2, with ability to function simultaneously as part of the known servo system for tracking and focusing. The feasibility of conjunction of this focusing device with other tunable element is also possible.
MEMS cells are the only tunable cells which have relatively wide ranges of tunability. However, MEMS are slow and mechanically unstable, and can""t be used for TDM or hetrodyne detection with very fast modulation. Therefore we also introduce a general approach for fabrication of tunable gratings over a large bandwidth of wavelengths; so that tunable gratings are used over wide ranges in the present invention.
While a variety of tunable cells can be used in the present invention, a preferred cell is based on Bragg gratings, which can not only combine wavelength demultiplexing with various homodyne functionalities, but in an analagous way (according to the Kogelnic theory) it can combine all forms of holographic demultiplexeing (Angular, Rotational, Shift, wavelength or their combination) with all the various homodyne functionalities and TDM. Examples to be considered involve phase sensitive detection combined with deflection sensitivity, which is a very important functionality for the optical microscopy, Also the combination of routing with time-division demultiplixing can be accomplished with the present invention.
As known in the field of holography and electro magnetic theory, either change in the wavelength or the beam direction, are considered as changes in the k-vector of the beam. In holography, grating efficiency is analogously sensitive in the K-vector variation, regardless of whether the variation comes from a change in the wavelength or the beam propagation direction or their combination. This should make any gratings devices based which can be implemented with wavelength variation also can be implemented with beam propagation direction variation or the combination.
The invention of K-wave selector based on thick Bragg gratings or holography can also have addition functionalities: (1) Spatial noise filtering ability. A significant feature for all diffusive microscopy and tomography as well as optical pick-up in multilayred data storage (2) wavefront de-encryption, a significant feature for atmospheric turbulence correction, and parallel microscopy and tomography. Wavefront deflection sensitivity is essential for numerous applications discussed herein such as microscopy, tomography, profilometry).
The term xe2x80x9cK-vectorxe2x80x9d along with Bragg matching, is discussed in one of the most fundamental papers in holography by Kogelnik, (H. Kogelnik Bell Syst.Tec.J 48,2909-2947 (1969). See for example, U.S. Pat. No. 5,438,439 to Mok et al at col. 4 among others. The length of the vector indicates wavelength and the orientation of the vector indicates beam direction. Either change in the input wavelength or in the beam direction represents a detectable variation in the K-vector of the input signal. The invention involves the use of tunable cells comprising for example: Bragg cells, Fabry-Perot etalons and it MEMS version, interferometers, holographic multiplexers such as (wavelength multiplexers, angular multiplexers, rotation multiplixers or their combination). These devices can operate in the transmissive mode where light is transmitted through the device or in the reflective mode, where the light is further transmitted by being reflected off of the device. Some applications shown in detail below, involve telecommunication, CD and DVD optical pickup devices, and microscopy. The Bragg cell is currently the preferred xe2x80x9cK-vector selectorxe2x80x9d for most of these applications, and the cell tuning source will preferably comprise a tuning cell control voltage source for producing an electrical control signal having a DC component and an incremental AC component. The DC component can select desired wavelengths or (K-vector and/or angle of incidence) of incoming light beams and the AC incremental component can initiate hetrodyne detection of a desired frequency, amplitude or phase modulated light beam by hetrodyning the AC component with the applied modulated light beam signal, and a time integrating CCD camera can completely retrieve the detected beam modulations representing the transmitted inrelligence. In the combined TDM and WDM (or K wavevector multiplixing) arrangement, the AC component turns the cell, preferably a Bragg cell on periodically during the time slots being demultiplexed or detected. In all embodiments, the AC component functions as a signal detector.
The invention employs a preferred method of demultiplexing a group of intelligence bearing light signals having different K-vectors and modulation K-vectors including the steps of: providing a K-vector selector (e.g. Bragg cell, volume hologram, interferometer) for simultaneously performing K-vector (e.g. wavelength) division demultiplexing and hetrodyne detection of selected K-vector modulated (e.g. frequency, phase or angle modulated) intelligence bearing light signals from the group of incoming intelligence bearing light signals, and applying an electrical control voltage (or appropriate tuning source such as stress, temperature, magnetic force, and mechanical motion) across the K-vector selector having a DC component for selectively tuning the K-vector selector to a selected transmission K-vector corresponding to a particular value of the DC component for causing the K-vector selector to transmit the light signal having such a selected transmission K-vector (e.g. wavelength), together with an AC component having a temporal signal for selectively producing heterodyne detection on the selected signal, and time integrating the resulting signal to complete demodulation of the selected signal.
The invention also provides an optical beam imaging (e.g. microscopy or tomography) optical pick-up detector comprising a K-vector selector having a holographic lens array or simple lenses therein for detecting a K-vector modulated oscillating optical image, together with a tuning control voltage source for applying an oscillating hetrodyne signal, phase locked with a frequency of oscillation of the optical image which can emerge from a probe, to the K-vector selector for causing the K-vector selector to hetrodyne detect the microscopic image; and a time integrating detector (e.g. CCD) for time integrating output signals from the K-vector selector tunable cell to complete demodulation of the hetrodyned signal. The preferred holographic lens array is produced. by interfering a number of point sources of light, displaced from each other, from a micro-scale fiber tip with a plane wave, and recording the resulting interference patterns within a tunable K-vector selector holographic element. For a number of applications of the invention, the wavelength transmission range or strength of the Bragg cell is greatly increased in accordance with the invention by forming a grating within the K-vector selector which is an encoded form of the composite of all individual gratings with their corresponding tuning levels required to multiplex the light beams.